1. Field of the Invention
This invention pertains generally to irrigation controllers and more particularly to an apparatus for expanding the number of timed stations which can be controlled from a single master control unit.
2. Description of the Background Art
Conventional timer operated irrigation controllers are manufactured with a fixed number of stations, each of which sequentially operates an electric solenoid valve to permit the flow of water to an area to be irrigated. In the event that more stations are required, a conventional controller cannot be expanded and, therefore, must be replaced with a larger unit. And, where very large areas are to be irrigated, it is typically impractical to manufacture a controller with a sufficient number of stations to provide for complete coverage. Therefore, in those instances it is common to utilize multiple controllers or a master/slave system where the master controller operates one or more slave units, but does not directly operate any valves. One such example can be found in the U.S. Pat. No. 4,244,022 issued to Kendall on Jan. 6, 1981. While a system such as this can be expanded by adding more slave units, up to a fixed number, when that limit is reached, further expansion is not possible since the slave units themselves cannot be expanded.
Various devices heretofore developed have certain limited capabilities for expanding the number of stations which can be controlled from a single station control line. For example, U.S. Pat. No. 4,661,719 issued to Burchfiel et al. on Apr. 28, 1987 discloses an auxiliary switching circuit which can be used to restore control functions in the event of a broken control line. The device is coupled to the master controller side of the broken control line and, drawing its power from the control line, is activated by the master controller during the time period that the valve connected to the broken control line would have been operated. One or more valves can be operated by the device, which includes internal control and clocking circuitry. However, because the device is powered by the control line from the master controller, it can only operate for a total period of time which does not exceed the station operation time set in the master controller. In many instances, this is limited to one hour. Furthermore, because of this limitation, it is not possible to cascade additional units for unlimited expansion of the system. And, if the control line is again broken or the master controller loses power, the device will become non-operational.
Therefore, a need exists for a device which can provide for expansion of an existing irrigation controller and provide for virtually unlimited expansion of the existing system. There is further a need for a device which can provide for timed control of the irrigation system even when the master controller is non-operational. The present invention satisfies that need and overcomes the deficiencies found in the devices heretofore developed.
The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicant's acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents teach or render obvious, singly or when considered in combination, applicant's claimed invention.